Semiconductor injection lasers such as that disclosed in IEEE, Journal of Quantum Electronics, Vol. QE-8, July 1972, pages 632-641 by Elisabeth M. Phillip-Rutz, have been developed for use in optical space navigation systems and optical communication systems, where the radiation is confined to the lower order transverse mode. For this mode control, the laser diode, with one or both of its cleaved mirror faces antireflection coated, is operated in an external optical cavity in which an aperture limiting slit is used to reduce the lifetime of all transverse modes except the lowest order mode. Although laser arrangement such as that disclosed in the Rutz Quantum Electronics article is a simple, compact means for generating coherent radiation from a semiconductor laser, its radiative power output is limited.
Workers in the field have attempted other approaches to increasing the power output of semiconductor laser devices. One approach is that used in U.S. Pat. No. 3,701,044 to Paoli and Ripper. The Paoli et al., patent discloses the optical coupling of adjacent stripe contact geometry semiconductor lasers, from which a spatially coherent beam may be obtained. The Paoli device obtains its mode control to the TEM.sub.00 mode by virtue of the narrow width of the respective laser stripes. The resonant cavity is formed by the cleaved end faces of the device. The coupling phenomenon is based upon optical leakage waves between adjacent stripe regions within the bulk of the device itself. The Paoli device appears to be limited in its spatially coherent power output because of the narrow width of the respective laser regions which are required for the mode control. What is needed in the art is a simple, compact semiconductor laser arrangement which efficiently generates a high radiative power output in a spatially coherent beam.